Because of a trend towards multi-chip modules, semiconductor manufacturers are required to supply unpackaged dice that have been tested and certified as known good die (KGD). Known good die is a collective term that denotes unpackaged die having the same reliability as the equivalent packaged die.
The need for known good die has led to the development of test apparatus in the form of temporary carriers suitable for testing discrete, unpackaged semiconductor dice. As an example, test apparatus for conducting burn-in tests for discrete die are disclosed in U.S. Pat. No. 4,899,107 to Corbett et al. and U.S. Pat. No. 5,302,891 to Wood et al., which are assigned to Micron Technology, Inc. Other test apparatus for discrete die are disclosed in U.S. Pat. No. 5,123,850 to Elder et al., and U.S. Pat. No. 5,073,117 to Malhi et al., which are assigned to Texas Instruments.
With this type of test apparatus, a non-permanent electrical connection must be made between contact locations on the die, such as bond pads, and external test circuitry associated with the test apparatus. The bond pads provide a connection point for testing the integrated circuitry formed on the die.
In making this temporary electrical connection, it is desirable to effect a connection that causes as little damage as possible to the bond pad. If the temporary connection to a bond pad damages the pad, the entire die may be rendered as unusable. This is difficult to accomplish because the connection must also produce a low resistance or ohmic contact with the bond pad. A bond pad typically includes a metal oxide layer that must be penetrated to make an ohmic contact.
Some prior art contact structures, such as probe cards, scrape the bond pads which wipes away the oxide layer and causes excessive damage to the bond pads. Other interconnect structures such as probe tips may pierce both the oxide layer and the metal bond pad and leave a deep gouge. Still other interconnect structures, such as microbumps, may not even pierce the oxide layer preventing the formation of an ohmic contact.
Another important consideration in testing of known good die is the effect of thermal expansion during the test procedure. As an example, during burn-in testing, a die is heated to an elevated temperature and maintained at temperature for a prolonged period. This causes thermal expansion of the die and temporary interconnect. If the die and the temporary interconnect expand by a different amount, stress may develop at the connection point and adversely effect the electrical connection. This may also lead to excessive damage of bond pads.
One type of semiconductor dice having a raised topology is referred to as a "bumped" die. A "bumped" semiconductor die includes bond pads formed with a bump of solderable material such as a lead-tin alloy. Bumped dice are often used for flip chip bonding wherein the die is mounted face down on a substrate, such as a printed circuit board, and then attached to the substrate by welding or soldering. Typically the bumps are formed as balls of material that are circular in a cross sectional plane parallel to the face of the die. The bumps typically have a diameter of from 50 .mu.m to 100 .mu.m. The sides of the bump typically bow or curve outwardly from a flat top surface. The flat top surface forms the actual region of contact with a mating electrode on the printed circuit board or other substrate.
In the past, following testing of a bumped die, it has been necessary to reflow the bumps, which are typically damaged by the test procedure. This is an additional process step which adds to the expense and complexity of the testing process. Furthermore, it requires heating the tested die which can adversely affect the integrated circuitry formed on the die.